Opioid analgesics such as morphine are therapeutically useful, but their usage is strictly limited because of their side effects such as drug dependency. Thus, analgesics with high usefulness and reduced tendency to cause drug dependency are desired. Considerable pharmacological and biochemical studies have been carried out to discover the opioid peptides and opioid receptors, and the dicovery of the subtype of opioid receptor such as .mu., .delta., .kappa. at a peripheral nerve in a variety of species, including human, has made a beginning towards creating new analgesics. As it is thought that opioid analgesics such as morphine act as a .mu.receptor agonist, separating the action based on a .kappa.-receptor agonist from the action based on .mu.-receptor agonist has been investigated. Recently .kappa.-selective agonists have been reported from the above viewpoint for example, EMD-60400: A. Barber et al., Naunyn-Schmled. Arch. Pharmacol., 345 (Suppl.): Abst 456. Some of them actually have been studied in clinical trials (Med. Res. Rev., 12, 525 (1992)).
However, even when a selective .kappa.-receptor agonist is employed, use of high doses can give rise to side effects such as sedation. Therefore, it would be desired to provide compounds having better agonist activity toward opioid .kappa.-receptor, and in particular compounds having only low sedative activity.